Method of maintaining edge strength of a piece of glass

ABSTRACT

A method of maintaining edge strength of a piece of glass i.e. preventing unintentional damage such as chips and/or scratches to the edges of the piece of glass during handling, processing and/or shipping is disclosed. A sheet of glass having dimensions greater than the desired size of the piece of glass is cut from a glass ribbon. The sheet of glass is pseudosubsurface scored or subsurface scored within the edges to define the piece of glass and to provide trim around the piece of glass which trim protects the edges of the piece of glass against unintentional damage. Thereafter, the sheet of glass is stored or processed, e.g., coating a surface of the sheet of glass with a transparent metal coating. The trim is removed from the sheet of glass at a fabrication station and the piece of glass having edges free of unintentional damage is used in the fabrication of a product e.g., a multiple glazed unit.

This is a continuation of application Ser. No. 566,545, filed Apr. 9,1975, which is a Division of application Ser. No. 438,096 filed Jan. 30,1974, now U.S. Pat. No. 3,956,547.

RELATED APPLICATIONS

The teachings of U.S. patent application Ser. No. 417,649 filed on Nov.20, 1973, in the name of Robert P. DeTorre and entitled"Pseudosubsurface Score" now U.S. Pat. No. 3,865,673; of U.S. patentapplication Ser. No. 242,511 filed on Apr. 10, 1972, in the names ofFred M. Ernsberger and Charles M. Hollabaugh and entitled "SubsurfaceCracks" now U.S. Pat. No. 3,865,293; of U.S. patent application Ser. No.159,746 filed on July 6, 1971, in the name of Helmut Franz and entitled"Angled Crossfire Rinses" now U.S. Pat. No. 3,793,054; of U.S. patentapplication Ser. No. 257,104 filed on May 26, 1972, in the name ofRobert P. DeTorre and entitled "Method of Cutting Glass and GlassArticles Made Thereby" now U.S. patent No. 3,795,572; of U.S. patentapplication Ser. No. 400,112 filed on Sept. 24, 1973, in the names ofGeorge H. Bowser, Renato J. Mazzoni and Raymond G. Gallagher andentitled "Method of Fabricating A Multiple Glazed Unit;" of U.S. Pat.Nos. 2,684,266, 2,974,377, 3,076,777, 3,756,104 and 3,760,997 may beused in the practice of the present invention and are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of maintaining edge strength of apiece of glass during handling, processing and/or shipping.

2. Description of the Prior Art

In the manufacture of architectural glass panels or multiple glazedunits, it is critical that the edges of the pieces of glass exhibitadequate edge strength e.g., the edge of the piece of glass preferablyshould have a modulus of rupture (MOR) greater than 2,700 pounds persquare inch (psi). This is particularly true for coated glass used assolar-absorbing glass because the difference in temperature between thecenter of the glass and the edge of the glass can generate tensilestresses at the edge of the glass of up to about 2,700 psi.

In this regard, consider the following. The center of thesolar-absorbing glass absorbs heat from the sun and expands. The edgesof the glass which are in the mounting frame are not exposed to the sunand therefore have a lower temperature. In certain instances, thetemperature of the glass at the center may be as much as 45° to 50° F.greater than at the edges of the glass for certain times of the day,e.g., in the morning. When glass is heated, it expands. Since the glassis hotter at the center than at the edges, the glass expands more at thecenter than at the edges. It has been found that edges of glass havingan MOR of greater than 2,700 psi have a higher probability ofwithstanding the tensile stresses acting at the edges of the glass thanedges of glass that have an MOR of less than 2,700 psi.

The prior art method of manufacturing solar-absorbing glass generallyincludes the steps of cutting a piece of glass to a desired size,coating the piece of glass with a transparent metal coating andassembling the piece of glass into a unit, e.g., a multiple glazed unit.

The prior art step of cutting normally includes scoring a sheet ofglass, removing trim from the sheet of glass and when necessary seamingthe edges of the piece of glass to remove scoring damage. As can beappreciated, scoring damage e.g., wing and/or spall, reduces the edgestrength of the piece of glass. This is because wing and/or spall arelocalized areas of high stress and are susceptible to generating a crackwhen put under tension.

The necessity of the seaming step and amount of seaming requiredgenerally depends on the type of scoring employed. For example (1)surface scoring i.e., a substantially perpendicular discontinuity in asheet of glass that extends or connects to a major surface of the sheetof glass and is bordered at the major surfaces by wing and/or spallrequires the seaming step to remove the edge damage caused by wingand/or spall; (2) subsurface cracking or subsurface scoring i.e., anessentially spall- or wing-free discontinuity or fissure, such as anintentially induced crack or score respectively that is within thethickness of a sheet of glass and extends substantially perpendicular tothe major surfaces of the glass but does not extend or connect to eitherof the major surfaces, requires less seaming, if any, because of theabsence of spall and/or wing; and (3) pseudosubsurface score i.e., anintentionally induced discontinuity or fissure in a sheet of glass thatextends substantially perpendicular to the major surfaces of the glassbut does not appear itself to extend or connect to either major surfaceof the glass. The pseudosubsurface score is accompanied by a zone ofdamaged glass which is essentially spall-or wing-free, which zone isdisposed between or extends between the tip end of the discontinuity anda major surface of the glass. Pseudosubsurface scoring requires lessseaming, if any, than surface scoring.

In each instance, the removal of edge damage induced by scoringincreases the edge strength of the piece of glass. However, it has beenfound, that the edge strength of the piece of glass can have an MORreduction of up to 1,000 psi after the cutting step and prior to usingthe piece of glass in fabrication of a unit. This reduction in edgestrength generally reduces the edge strength of the piece of glass belowan MOR of 2,700 psi thereby making the piece of glass susceptible tocracking.

This reduction of edge strength is attributed to unintentional damagee.g., chips and/or scratches, to the edges of the piece of glass whichunintentional damage occurs during handling, processing and/or storingof the piece of glass. The edges of the piece of glass can be damagedfor example (1) when the piece of glass is loaded on or removed from acoating apparatus or (2) by chips of glass or abrasive particles onrubber pads which support the glass for shipping or storing. The chipsor scratches act as localized areas of stress and the piece of glasscracks by the mechanism previously discussed.

To prevent unintentional damage to the edges of the piece of glass, itis possible to handle the pieces of glass with extreme care. However,this does not prevent accidents from occurring which can cause edgedamage to the pieces of glass. Further, increased care in handling tendsto increase the cost of the finished unit.

SUMMARY OF THE INVENTION

This invention relates to a method of protecting at least one edge of apiece of frangible material e.g., glass, during handling e.g., coatingor washing, to prevent unintentional edge damage e.g., chips andscratches which occur during handling, processing and/or storing to theat least one edge. The method including the steps of providing a sheetof glass having dimensions greater than at least one dimension of thepiece, scoring the sheet of glass to provide a score such that the atleast one edge of the piece is provided with trim. The score is of thetype that does not heal e.g., subsurface score, pseudosubsurface score.The sheet of glass is handled e.g., coated or washed and edge damagenormally associated with handling is to the trim and not to the at leastone edge of the piece of glass.

Prior to using the piece of glass in manufacturing e.g., fabricating amultiple glazed unit, the trim is removed by applying a bending moment.Any unintentional damage to the glass such as chips and/or scratheswhich tend to reduce the edge strength are to the edges of the trim andnot the at least one edge of the piece of glass. In this manner, theedge strength of the glass is maintained.

Further, this invention relates to an article of manufacture made inaccordance to the teaching of the invention.

Further, this invention relates to a method of protecting at least oneedge of piece of frangible material e.g., glass, during coating. A sheetof glass is scored to define the piece within the sheet and to providetrim on at least one edge of the piece of glass. During coating,unintentional edge damage is to the trim and not to the piece of glass.After coating the trim is removed.

Further, this invention relates to an improved method of fabricatingmultiple glazed units. The improvement includes scoring each of twosheets of rigid material e.g., glass, to define a piece of glass withineach of the sheets and to provide trim on at least one edge of the pieceof glass. The sheets of glass are subsequently stored, coated and/orwashed. Any unintentional edge damage during storing, coating and/orwashing is to the trim and not to the piece of glass. Prior to using thesheets of glass in fabricating the unit, the trim is removed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating preferred procedural steps of theinvention;

FIG. 2 is a view of a major surface of a sheet of glass scored inaccordance to one embodiment of the invention;

FIG. 3 is an elevation view of a cutting wheel running apseudosubsurface score in a sheet of glass and having portions removedfor purposes of clarity;

FIG. 4 is a view of a major surface of a sheet of glass scored inaccordance with an alternate embodiment of the invention;

FIG. 5 is a similar view as FIG. 2 showing the sheet of glass scored todefine two pieces of glass;

FIG. 6 is an elevation view of a snapping apparatus in position to applya bending moment about a pseudosubsurface score; and

FIG. 7 is an isometric view of a multiple glazed unit fabricated inaccordance to the teachings of the invention.

DESCRIPTION OF THE INVENTION

With reference to FIG. 1, there is shown a flow diagram of proceduralsteps that may be taken to practice the invention. As will beappreciated by those skilled in the art, the flow diagram is onlyillustrative of procedural steps that may be taken in the practice ofthe invention and therefore, the invention is not limited thereto.Further, the discussion of the invention will be directed to sheets ofglass. However, as will become apparent, the invention is not limitedthereto and may be practiced on sheets of any frangible material.

As shown in FIG. 1, the first step is to provide a sheet of glass havingdimensions greater than a desired size of a piece of glass to be used infabrication e.g., in the manufacture of a multiple glazed unit. Forexample, if the piece of glass is to have a dimension of 6 feet × 10feet, the sheet of glass would preferably have dimensions of between61/3 feet × 101/3 feet and 7 feet × 11 feet respectively. This willprovide the piece of glass with approximately 2 to 6 inches of trimaround its edges.

The sheet of glass, if desired, may be coated witnh a transparent oropaque coating. As can be appreciated, the invention is not limited tothe surface preparation of the sheet of glass.

The next step of the invention as shown in FIG. 1 is to score the sheetof glass 10 within its edges to define a piece of glass 12 having thedesired dimensions to provide the piece of glass 12 with trim 14 (seeFIG. 2).

It is recommended that the sheet of glass be scored in such a mannerthat the score does not heal. In other words, after the passage of timee.g., up to 3 months, the trim can be removed from the sheet of glass ata fabrication station without the necessity of rescoring the sheet ofglass. It is believed that a score heals because the stresses producedby the scoring action disappear and the cut is more difficult to open.The advantages of scoring the sheet to define the piece of glass in sucha manner that the score does not heal will be discussed in more detailbelow.

Types of scores that do not heal, but not limited thereto are (1) apseudosubsurface score as taught in U.S. patent application Ser. No.417,649 filed on Nov. 20, 1973, in the name of Robert P. DeTorre andentitled "Pseudosubsurface Score" now U.S. Pat. No. 3,865,673; and (2) asubsurface score or crack as taught in U.S. patent application Ser. No.242,511 filed on Apr. 10, 1972, in the names of Fred M. Ernsberger andCharles M. Hollabaugh and entitled "Subsurface Cracks" now U.S. Pat. No.3,865,293. A pseusosubsurface score or a subsurface score is preferredfor scoring the glass because (1) the score does not heal and (2)normally no seaming of the edges is required after the trim is removedbecause the edges are essentially free of score damage e.g., wing and/orspall.

For purposes of illustration, the discussion of the invention will bedirected to pseudosubsurface scoring. However, as will be appreciated,the invention is not limited thereto.

With reference to FIG. 3, there is shown a scoring or cutting wheel 16rotatably mounted on a shaft 18. The shaft 18 passes through a centralaxle hole 20 of the scoring wheel and is securely mounted at its ends toa fork member 22. One skilled in the art will appreciate that there aremany commercially available devices for housing scoring wheels, such aswheel 16 and for supplying a load to the scoring wheel. It is wellknown, for example, that the necessary scoring force can be applied to ascoring wheel by means of fluid pressure such as air or hydraulic fluid.Further, U.S. Pat. Nos. 3,756,104 and 3,760,997 suggests that a scoringwheel may be actuated by a constant-reluctance motor.

The wheel 16 is preferably made of tungsten carbide or other suitablematerial having a hardness of about 7 or more on Mohs scale. The wheel16 has a pair of generally parallel outer surfaces 24 and 26 aboutscoring surface 28. The scoring surface 28 generally includes sides 30and 32 which if extended form a base angle of approximately 120°. Acutting angle is formed by sides 36 and 38. To provide apseudosubsurface score 40 in the sheet of glass 10 which is generallyperpendicular to a major surface e.g., surface 42 of the sheet of glass,it is recommended that angles A and B formed by the sides 36 and 38 andthe surface 42 of the sheet of glass 10 be equal.

The cutting angle is preferably between approximately 155° andapproximately 165°, with approximately 157° to 163° providing optimumresults. The diameter of the cutting wheel is at least approximately 1/2inch and preferably between approximately 3/4 inch and 2 inches. Theforces applied to the scoring wheel 16 is between approximately 65 and600 pounds and preferably between approximately 80 and 300 pounds. Therecommended speed of the scoring wheel is between about 60 and 360inches per minute and preferably between approximately 90 and 250 inchesper minute.

Referring to Table I, there is shown the ranges of force for scoringwheels of various diameters each having a scoring angle of 163° theapproximate maximum recommended speeds for each wheel and the depths ofpseudosubsurface scores in glass supported on a flat, hard cutting bede.g., mounting the sheet of glass on a 1/16 inch line contact under thesheet of glass for support.

                                      TABLE II                                    __________________________________________________________________________    Wheel Diameter, Range of Force, Range of Depth of the Pseudosubsurface        Score and Maximum Scoring Speed for Scoring Wheels Having a                   Scoring Angle of 163°                                                  __________________________________________________________________________                     Range of Depth                                               Wheel Diameter                                                                         Range of Force                                                                        Pseudosubsurface Score                                                                    Maximum Scoring                                  Inches   Pounds  Inches      Speed Inches/Second                              __________________________________________________________________________    0.50      65-250 0.060 - 0.080                                                                             1.00                                             0.75      80-300 0.060 - 0.100                                                                             1.50                                             1.25     125-350 0.065 - 0.105                                                                             3.00                                             2.00     180-450 0.080 - 0.120                                                                             4.00                                             4.00     225-600 0.105 - 0.160                                                                             6.00                                             __________________________________________________________________________     *Based on results with 1/16 inch line contact under the glass surface for     support                                                                  

With reference to FIG. 3, the sheet of glass 10 is positioned on a rigidsupport 44 e.g., a flat, hard cutting bed. The support 44 is providedwith a line contact 45 e.g., a 1/16 inch high rib.

A series of pseudosubsurface scores is made within the edges of thesheet of glass 10 to define the piece of glass 12 and to provide trim 14around the piece of glass (see FIG. 2).

In general, the width of the trim 14 is a function of the glassthickness and the distance between the surface engaged by the scoringwheel e.g., surface 42, in FIG. 3 and bottom tip 46 of thepseudosubsurface score 40. As the distance between the surface 42 andthe tip 46 of the score 40 increases for sheets of glass of the samethickness, the width of the trim 14 should be decreased. As the width ofthe trim 14 increases, less bending moment is required to snap the trimfrom the piece of glass. This is because as the width increases, theweight of the trim increases. Further, as the width of the trimincreases, the lever arm i.e., the distance from the score to theadjacent edge of the sheet of glass increases and less force is requiredto snap the trim. In certain instances, the trim can be snapped duringhandling and cause injury. Conversely reducing the width of the trimwhile reducing the distance between surface 42 and the tip 46 of thescore 40 (see FIG. 3) for glass sheets having the same thickness toprevent accidental snapping of the trim from the sheet of glassminimizes the advantage of the weight of the trim during the step ofremoving the trim from the sheet of glass.

With reference to Table II, there is shown preferred minimumpseudosubsurface score depths i.e., the distance between surface 42 andthe tip 46 of the score 40, as shown in FIG. 3, for various glassthicknesses and the recommended width of the trim.

                  TABLE II                                                        ______________________________________                                        Preferred Minimum Depth of Score and Preferred                                Width of Trim for Pieces of Glass Having                                      Varying Glass Thicknesses                                                               Preferred Minimum Depth                                                                         Preferred Width                                   Glass Thickness                                                                         of Pseudosubsurface Score                                                                       of Trim                                           Inches    Inches            Inches                                            ______________________________________                                        0.25      0.040 -  .075     2                                                 0.50      0.075 - 0.125     2                                                 0.75      0.125 - 0.180     4                                                 1.00      0.180 - 0.250     6                                                 ______________________________________                                    

Although the invention is not limited thereto, it is recommended tofacilitate the start of the pseudosubsurface score that the initialforce applied to the scoring wheel be approximately 20 percent greaterthan the selected scoring force. For example, to initiate the score 40(see FIG. 3) the pressure should be 20 percent greater and after thescore is run for about 1/8 inch, the force is reduced to the selectedscoring force. Another recommended method of initiating thepseudosubsurface score 40 is to initially impact the surface 42 of thesheet of glass 10 with a force which is about 20 percent greater thanthe selected scoring force.

Although it is not completely understood, it has been found thatoccasionally when a second pseudosubsurface score crosses a firstpreviously made pseudosubsurface score and the trim removed along thesecond score prior to removing trim along the first score, the trimsnapped along the second score deviates from the second score at thecross over between the first and second score. To avoid the problem oftrim deviating from the score line, the following is recommended.

A first score may be made from one edge of the sheet to the oppositeedge. Subsequent scores may begin from previous scores e.g., a secondscore starts from the first score and extends to the farthermost edge.Further, it is recommended that the trim be run along the score lines inthe sequence in which the scores were made. For example, and withreference to FIG. 2, score 47 extends from edge 48 to edge 50 of thesheet of glass 10. Score 52 extends from the score 47 to the edge 54 ofthe sheet of glass 10. Score 56 extends from the score 52 to the edge 48of the sheet of glass 10. Score 58 extends from the score 56 and extendsto the edge 60.

The trim 14 is then removed by sequentially running score lines 47, 52,56 and 58. Another scoring procedure will be discussed. With referenceto FIG. 4, a sheet of glass 70 is scored to provide trim 71 byinitiating a score 72 at edge 74 and running the score 72 to edge 76 ofthe sheet of glass 70. A score 78 initiated at edge 79 is run to thescore 72. A score 80 is initiated at the score 72 and run to the edge 82of the sheet of glass 70. A score 84 is initiated at the edge 76 and isrun to the score 80. A score 86 is initiated at the score 80 and run tothe edge 74 of the sheet of glass 70. A score 88 is initiated at theedge 82 and run to the score 86. Score 90 is initiated at the score 86and run to the score 72. Score 92 is initiated at the score 72 and runto the edge 79 of the sheet of glass 70.

The trim 71 of the piece of glass can be removed from the sheet of glassalong any selected one of the scores and need not be snapped inaccordance with the sequence at which the sheet was scored.

Although two illustrations are presented for providing trim on a sheetof glass, it can be appreciated by those skilled in the art that theinvention is not limited thereto.

With reference to FIG. 5, there is shown another embodiment of theinvention. More particularly, providing edge protection for a pluralityof pieces of glass 96 and 100. In this instance, the sheet of glass hasdimensions greater than a plurality of the pieces of glass. A sheet ofglass 102 is scored in a similar manner as sheet 10 was scored (see FIG.2) to provide trim around the edges of the pieces of glass 96 and 100.Thereafter a pseudosubsurface score 104 is initiated at score 56 and runto the edge 60 to provide the sheet of glass 102 with the two pieces ofglass 96 and 100. In this instance, the trim 14 is first removed, aspreviously discussed, and thereafter the pieces of glass 96 and 100 areseparated. Since the score 47 was made prior to score 104, the trim willnot deviate from the score 46 when the trim 14 is snapped along thescore 47.

As can be appreciated, by providing several pieces of glass within asheet of glass, the amount of handling is reduced. More particularly,and with reference to FIG. 5, instead of handling 2 discrete sheets ofglass e.g., two sheets of glass 10 having the piece of glass 12 (seeFIG. 2), it is possible to handle a single sheet of glass e.g., thesheet 102 having two pieces of glass 96 and 100. Further, a savings inmaterial is realized because of the reduction in the amount of trim.

Although the preceding discussion was directed to providing trim aroundthe edges of the piece of glass, it can now be appreciated by thoseskilled in the art that if only one edge of the piece of glass hasunintentional edge damage e.g., chips and/or scratches that occur duringhandling, processing and/or storing, it is possible to provide trim onlyon that edge that continually exhibits unintentional edge damage.

Referring back to FIG. 1, the scored sheet of glass may be furtherprocessed by coating a transparent metal coating on the surface in anywell known manner such as that taught in U.S. patent application Ser.No. 159,746 filed on July 6, 1971, in the name of Helmut Franz andentitled "Angled Crossfire Rinses" now U.S. Pat. No. 3,793,054. In thealternative, if the sheet of glass has a coating already on the surface,it would be directly stored or shipped to a fabrication station.Further, in the alternative, if the sheet of glass is clear and it isnot desired to apply a coating to the surface, then the clear sheet ofglass would be stored or shipped to a fabrication station.

Unintentional edge damage e.g., chips or scratches, that normally occurduring handling, processing and/or shipping which reduces edge strengthoccurs to the edges of the sheet of glass i.e., to the edges of thetrim, and not to the edges of the piece of glass. In this manner, theedge strength of the piece of glass is a function of the cutting methodand can be easily controlled.

When it is required to use the piece of glass, the trim is removed fromthe sheet. With reference to FIG. 6, there is shown an elevation view ofa snapping apparatus 110 in position to apply a bending moment about thepseudosubsurface deep score 40. The apparatus may consist of two topanvils 112 and 114 and a bottom anvil 116. The top anvils 112 and 114are positioned against the surface 42 of the sheet of glass about thescore 40. The anvil 116 is positioned against surface 120 of the sheetof glass aligned with the score 40. Thereafter, the anvils 112 and 114are urged downward as the anvil 116 is urged upward as viewed in FIG. 6to apply a bending moment to remove the trim.

The trim can also be removed by placing the sheet of glass 10 upon atable so that the trim and a portion of the pseudosubsurface score 40overlaps the table. A bending moment may be applied to the trim whichoverlaps the table to run a cut along the pseudosubsurface score 40.

It is sometimes difficult, especially with sheets of glass that arerelatively long and thick e.g., 0.75 inch thick glass in excess of 10feet in length, to run a cut in the manner described. Under suchcircumstances, the tapping and/or heating and/or bending momentprocedures disclosed in U.S. patent application Ser. No. 257,104 filedon May 26, 1972, in the name of Robert P. DeTorre and entitled "Methodof Cutting Glass and Glass Articles Made Thereby" now U.S. Pat. No.3,795,572 may be employed. Further, the trim may be removed by placing asolid plate approximately 1/2 inch in width between the glass and thetable directly beneath the pseudosubsurface score 10 and applying abending moment to the trim.

Use of the procedure of application Ser. No. 257,104 now U.S. Pat. No.3,795,572 broadly involves applying a tap to the bottom of the score topropagate the score deeper into the piece and/or applying heat along thelength of the top of the score to propagate the score deeper into thepiece. Thereafter either (1) heat is applied along the bottom of thescore to further propagate the score while a bending moment is appliedabout the score to fracture a remaining thin zone of glass or (2) heatis applied along the bottom of the score to fracture the glass or abending moment is applied about the score without bottom heating.

Alternatively, use of the narrow plate or member places the top surfaceof the piece of glass in tension along the score and reduces the energynecessary to run a cut along the entire length of the piece.

Referring back to FIG. 1 after the trim has been removed, a unit e.g., amultiple glazed unit can be fabricated with the piece of glass.

In general, a pseudosubsurface score or subsurface score or fractureprovides the piece of glass with pristine edges having an MOR of greaterthan 2,700 psi and therefore no seaming is required.

As can now be appreciated, by practicing the method of the invention theedge strength of a piece of glass is maintained. This is because anyunintentional edge damage e.g., chips and/or scratches, which reduceedge strength occur to the edges of the trim and not to the edge of thepiece of glass.

Processing sheets of glass and providing cutting equipment at each of aplurality of fabrication stations is not economically feasible.Processing pieces of glass and thereafter removing edge damage caused bycutting and unintentional edge damage by seaming has two drawbacks;namely (1) the seaming step has to be performed to remove all edgedamage and (2) tight tolerances of pieces of glass cannot be easilymaintained because the amount of seaming depends on the edge damage.

Although the discussion was directed generally to rectangular or squareshaped sheets of glass, it can be appreciated that the invention is notlimited thereto. More particularly, the method of this invention may beused to prevent unintentional edge damage to windshield blanks.

DETAILED DESCRIPTION OF THE INVENTION

The method of the invention will now be described to fabricate amultiple glazed unit 122 shown in FIG. 7. The unit 122 includes a pieceof glass 124 coated with a transparent metal coating 126 on surface 128of a piece of glass and a clear piece of glass 12. The pieces of glassused to fabricate the multiple glazed unit are required to havedimensions of 6 feet × 10 feet and a thickness of approximately 1/4inch.

Two sheets of glass 10 are provided each approximately 61/3 inches ×101/3 inches. With reference to FIG. 3, a scoring wheel 16 having adiameter of 3/4 inch and a cutting angle of 163° will be used topseudosubsurface score the sheets of glass. A force of 300 pounds isapplied to the wheel 16 to provide a pseudosubsurface score 40 betweenmajor surfaces 42 and 120 of the sheets of glass.

With reference to FIGS. 2 and 3, the sheet of glass 10 is positioned ona flat hard cutting bed 44 having a 1/16 inch line contact 45. Thesurface 120 engages the line contact 45 about 2 inches from edge 60 ofthe sheet of glass. The wheel 16 is positioned at edge 48, 2 inches fromthe edge 60 and above the line contact 45. The force acting on the wheelis 360 pounds to initiate the score 47. The wheel is moved about 1/8"toward the edge 50 of the sheet of glass, in any conventional manner asthe force is dropped to 300 pounds. The score 47 is run to the edge 50under a force of 300 pounds. The wheel 16 is then positioned at thescore 46 spaced 2" from the edge 50 and above line contact 45. A score52 is run from the score 47 toward the edge 54 of the sheet of glass 10in a similar manner as score 47 was run. The wheel 16 is then placed atthe score 52 spaced 2" from the edge 54 of the sheet of glass 10 andabove the line contact 45. A score 56 is run from the score 52 towardedge 48 of the sheet of glass in a similar manner as the score 47 wasrun. The wheel 16 is then placed at the score 56 spaced 2" from the edge48 and above the line contact 45. A score 58 is run from the score 56toward the edge 60 of the sheet of glass in a similar manner as thescore 47 was run.

The above scoring procedure is repeated on the second sheet of glass toprovide two sheets of glass each having 2" of trim about a piece ofglass 12 having dimensions of 6 feet × 10 feet.

Thereafter, a coating is applied to one surface of a sheet of glass in amanner disclosed in the above-mentioned U.S. patent application Ser. No.159,746 now U.S. Pat. No. 3,793,054 to provide a sheet of glass havingthe piece of glass 124 with the coating 126 on the surface 128 (see FIG.7). During the coating of the surface 128 any unintentional edge damageoccurs to the edges of the trim and not to the edges of the piece ofglass 124. In this manner, the edge strength of the piece of glass 124is maintained.

The sheet of glass having a coated surface and the other sheet of glassare shipped to a fabrication station designated for fabricating multipleglazed units. During the handling and/or shipping of the sheets ofglass, any unintentional edge damage is to the edges of the trim and notto the edges of the pieces of glass thereby maintaining the edgestrength of the pieces of glass.

At the fabrication station the sheets of glass are washed in anyconventional manner to clean the surfaces. During the washing,unintentional edge damage occurs to the edges of the trim and not to theedges of the pieces of glass. Thereafter, the trim is mechanicallyremoved from the sheets of glass by applying a bending moment to providetwo pieces of glass 10 and 126 having dimensions of 6 feet × 10 feet andhaving edges free of unintentional edge damage.

More particularly and with reference to FIGS. 2 and 6, a pair of anvils112 and 114 are positioned in from the edge 48 of the sheet of glass 10about the score 47 and against the surface 42. An anvil 116 ispositioned against surface 120 of the sheet of glass 10 aligned with thescore 46.

With reference to FIG. 6, the anvils 112 and 114 are moved downward asthe anvil 116 is moved upward as viewed in FIG. 6 under a force of 16inches-pounds to apply a bending moment to the trim 14. To facilitatethe propagation of the score 47 to the major surfaces 42 and 120 theedge 48 at the score 47 may be tapped with a rigid member beforeapplying the bending moment.

In a similar manner, and in sequence, scores 52 and 56 and 58 arepropagated to major surfaces of the sheet of glass to remove the trim.

Thereafter, the pieces of glass are used in the fabrication of amultiple glazed unit fabricated in any conventional manner.

For example, and with reference to FIG. 7, there is shown the multipleglazed unit 122 having the coated piece of glass 124 and the clear pieceof glass 12 arranged in parallel relationship. The glass sheets areseparated at their marginal edges by a continuous metal spacer element130 such as disclosed in U.S. Pat. No. 2,684,266. The spacer elementincludes a generally rectangular cross-sectional tubular portion that isfilled with a desiccant 132. An example of a suitable desiccant isgranular or powdered silica gel. Communication between the air spacebetween the pieces of glass 12 and 124 and the desiccant 132 is providedthrough a plurality of channels or passages 134 in the spacer element130. The spacer element 130 extends completely around the unit 122 andbetween the marginal edges of the glass sheets.

The spacer element 130 is adhered to the glass sheets 12 and 126 attheir inner faces by way of a thin continuous film of an adhesive,moisture-resistant mastic composition 136 such as disclosed in U.S. Pat.Nos. 2,974,377 and 3,076,777 to form a primary moisture resistant seal.The primary seal may be formed in any conventional manner such as thattaught in U.S. patent application Ser. No. 400,112 filed on Sept. 24,1973, in the names of George H. Bowser, Renato J. Mazzoni and Raymond G.Gallagher and entitled "Method of Fabricating a Multiple Glazed Unit."

In addition, a resilient, moisture-resistant strip 138 with a layer ofmastic 140 adhered thereto, such as disclosed in U.S. Pat. No. 2,974,377is bonded to the peripheral edge or flat side 142 of the spacer element130 and the peripheral edges of the pieces of glass in any conventionalmanner. Strip 138 and mastic 140 extend completely around the perimeterof the unit.

A channel member 144 of essentially U-shaped cross-section also extendscompletely around the perimeter of the unit to protect the edges. Thechannel member 144 generally includes several sections of channelingthat are joined or butted together at their ends.

As can be appreciated, by practicing the method of this invention, anyunintentional edge damage that occurs during the coating, shipping,storing and/or handling will be to the edges of the trim and not to thepieces of glass. By providing that the unintentional edge damage occursto the trim and not to the pieces of glass, the MOR of the edges of thepiece of glass is a function of the method of cutting and is not reducedby chipping and/or scratching normally occurring to the edges duringintermediate processes or handling.

What is claimed is:
 1. A method of protecting the peripheral edges of aflat piece of refractory material selected from the group consisting ofglasses, ceramics and glass-ceramics during a coating operation,comprising the steps of:providing a flat sheet of refractory materialhaving four sides and peripheral dimensions greater than the peripheraldimensions of the piece and having a surface area greater than thesurface area of the piece to be coated; scoring the sheet from a firstside to a second side of the sheet opposite to the first side to providea first score line on the sheet between the first and second sides ofthe sheet; scoring the sheet from the first score line to a third sideof the sheet to provide a second score line between the first score lineand the third side of the sheet; scoring the sheet from the second scoreline to the first side of the sheet to provide a third score linebetween the second score line and the first side of the sheet; scoringthe sheet from the third score line to a fourth side of the sheet toprovide a fourth score line between the third score line and fourth sideof the sheet wherein the piece of refractory material is defined by thefirst, second, third and fourth score lines and the piece of refractorymaterial has trim on each side; and wherein the first, second, third andfourth score lines are each a discontinuity within the thickness of thesheet and are each essentially free of wing or spall; and coating asurface of the piece while the trim protects the piece from edge damage;and running the first, second, third and fourth score lines in thesequence in which the score lines were made to remove the trim from thepiece.
 2. The method as set forth in claim 1 further including the stepof positioning the coated sheet of refractory material with peripheraledge portions of the trim in surface engagement with a base wherein saidpositioning step is practiced before said running step.
 3. The method asset forth in claim 1 wherein said scoring step further includes the stepof:scoring the defined piece of refractory material between a pair ofopposed score lines to define at least two pieces of refractorymaterial; and practicing said step of scoring the defined piece prior tosaid coating step.
 4. The method as set forth in claim 3 furtherincluding the step of:separating the at least two pieces of refractorymaterial; and practicing said separating step after said running step.